// C# implementation of recursive Binary Search 
using System; 
  
class BinarySearch { 
    // Returns index of x if it is present in 
    // arr[l..r], else return -1 
    static int binarySearch(int[] arr, int l, 
                            int r, int x) 
    { 
        if (r >= l) { 
            int mid = l + (r - l) / 2; 
  
            // If the element is present at the 
            // middle itself 
            if (arr[mid] == x) 
                return mid; 
  
            // If element is smaller than mid, then 
            // it can only be present in left subarray 
            if (arr[mid] > x) 
                return binarySearch(arr, l, mid - 1, x); 
  
            // Else the element can only be present 
            // in right subarray 
            return binarySearch(arr, mid + 1, r, x); 
        } 
  
        // We reach here when element is not present 
        // in array 
        return -1; 
    } 
  
    // Driver method to test above 
    public static void Main() 
    { 
  
        int[] arr = { 2, 3, 4, 10, 40 }; 
        int n = arr.Length; 
        int x = 10; 
  
        int result = binarySearch(arr, 0, n - 1, x); 
  
        if (result == -1) 
            Console.WriteLine("Element not present"); 
        else
            Console.WriteLine("Element found at index "
                              + result); 
    } 
} 